Density unevenness reduction method and sheet transport mechanism

ABSTRACT

A density unevenness reduction method of a printing apparatus having a sheet transport mechanism which transmits a driving force of a driving device to a roller via a plurality of gears to drive the roller for transporting a sheet, the method includes: assuming one tooth and one turn of each of the gears each to be a simple harmonic oscillation of a single sine wave, and generating a synthesized wave of the sine waves of the gears; and adjusting the module and the number of teeth of each of the gears, thereby dispersing a frequency at which the oscillations of the gears overlap and are amplified in the synthesized wave.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention contains subject matter related to and claimspriority to Japanese Patent Application No. 2009-021269 filed in theJapanese Patent Office on Feb. 2, 2009, the entire contents of which isincorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

1. Technical Field

The present disclosure relates to a density unevenness reduction methodof a printing apparatus including a sheet transport mechanism whichtransmits a driving force of a driving device to a roller fortransporting a sheet via a plurality of gears, and the sheet transportmechanism.

2. Related Art

In the past, in a printing apparatus, a sheet transport mechanism whichtransmits a driving force of a drive motor as a driving device to aroller used for transporting a sheet such as a platen roller or a paperfeed roller via a plurality of gears so as to rotate the roller has beenused.

In the sheet transport mechanism of the printing apparatus, there is aconcern that errors in gear mesh occur for each tooth and for each turnof the gears for transmitting the driving force of the drive motor tothe platen roller or the paper feed roller, resulting in a change inpaper feed speed. When a change in the paper feed speed occurs in thesheet transport mechanism, there is a concern that density unevenness,which is called jitter, may occur in an image that can be obtained bythe printing apparatus.

Therefore, in order to obtain an image with high quality by reducing thegeneration of jitter, in Japanese Unexamined Patent Application No.11-295949, a drive transmission mechanism in which gear mesh frequenciesare different from each other is disclosed. In addition, in JapaneseUnexamined Patent Application No. 2002-189325, a driving deviceincluding a rotor in which the module and the number of teeth of a largegear are different from those of a small gear in a multiple-gear isdisclosed.

However, in the case where the gear mesh frequencies are different fromeach other in the drive transmission mechanism disclosed in JapaneseUnexamined Patent Application No. 11-295949, over a short period, it ispossible to reduce the amplitude of the mesh frequencies. However, overa long period, there may be a case where the gear mesh frequenciesoverlap and the amplitude of the frequencies increases, so that there isa problem in that whizzing may occur in the drive transmission mechanismover a long period and jitter may be generated.

In addition, even in the case where the module and the number of teethof the large gear are set to be different from those of the small gearin the multiple-gear of the rotor of the driving device disclosed inJapanese Unexamined Patent Application No. 2002-189325, as in the drivetransmission mechanism of Japanese Unexamined Patent Application No.11-295949, there is a concern that over a long period, the gear meshfrequencies overlap and the amplitude of the frequencies increases,whizzing occurs, and jitter may be generated.

Moreover, improving precision in tooth shapes and engagement of gears toreduce errors in gear mesh and prevent the generation of jitter may beconsidered. However, with the improvement of the precision of the gears,production costs are increased.

These and other drawbacks exits.

SUMMARY OF THE DISCLOSURE

It is desirable to provide a density unevenness reduction method and asheet transport mechanism capable of reducing errors in gear mesh over along period to suppress a change in paper feed speed so as to reduce thegeneration of density unevenness such as jitter without an increase inproduction costs, thereby obtaining an image with high quality.

According to an embodiment, there is provided a density unevennessreduction method of a printing apparatus having a sheet transportmechanism which transmits a driving force of a driving device to aroller via a plurality of gears to drive the roller for transporting asheet. The method includes: assuming one tooth and one turn of each ofthe gears each to be a simple harmonic oscillation of a single sinewave, and generating a synthesized wave of the sine waves of the gears;and adjusting the module and the number of teeth of each of the gears soas not to allow the amplitude of the frequencies of the synthesized waveto be significant over a long period, thereby dispersing a frequency atwhich the oscillations of the gears overlap and are amplified in thesynthesized wave.

Here, the long period in this aspect is not a period for each tooth oreach turn of an individual gear but indicates a period of whizzing thatoccurs when the synthesized wave of the gears is generated.

In addition, the statement that the amplitude of the frequency of thesynthesized wave is not significant means that sharp peaks and regularpeaks do not exist in the synthesized sine wave.

According to this embodiment, errors in engagement of gears can bereduced when the printing apparatus prints on a sheet while the sheettransport mechanism transports the sheet, thereby suppressing a changein paper feed speed.

According to vairous embodiments, there is provided a sheet transportmechanism including: a roller used for transporting a sheet; a drivingdevice for driving the roller; and a plurality of gears for transmittinga driving force of the driving device to the roller, wherein, assumingone tooth and one turn of each of the gears each to be a simple harmonicoscillation of a single sine wave, a synthesized wave of the sine wavesof the gears is generated; and the module and the number of teeth ofeach of the gears are adjusted so as to disperse a frequency at whichthe oscillations of the gears overlap and are amplified in thesynthesized wave and shortens the amplitude of the frequency of thesynthesized wave over a long period.

Here, the long period in this aspect is not a period for each tooth oreach turn of an individual gear but indicates a period of whizzing thatoccurs when the synthesized wave of the gears is generated.

In addition, the statement that the amplitude of the frequency of thesynthesized wave is not significant means that sharp peaks and regularpeaks do not exist in the synthesized sine wave.

According to this embodiment, errors in engagement of gears can bereduced when the printing apparatus prints on a sheet while the sheettransport mechanism transports the sheet, thereby suppressing a changein paper feed speed.

Also, the roller is a paper feed roller disposed on at least one of theupstream side and the downstream side of a platen roller in a transportdirection of the sheet.

Accordingly, the sheet transport mechanism can reduce errors inengagement of gears when the printing apparatus prints on a sheet whilethe sheet transport mechanism transports the sheet, thereby suppressinga change in paper feed speed.

In this embodiment, the paper feed roller is configured as a projectionroller of which a plurality of projection teeth engaged with the teethof one of the gears are arranged in parallel with the circumferentialdirection of the paper feed roller, assuming one projection tooth andone turn of the paper feed roller each to be a simple harmonicoscillation of a single sine wave, a synthesized wave of the sine wavesof the gears and the paper feed roller is generated, and the size of thepaper feed roller and the number of projection teeth are set so as todisperse a frequency at which the oscillations of the gears and thepaper feed roller overlap and are amplified in the synthesized wave soas to shorten the amplitude of the frequency of the synthesized waveover a long period.

Accordingly, the sheet transport mechanism can reduce errors inengagement of gears when the printing apparatus prints on a sheet whilethe sheet transport mechanism transports the sheet, thereby suppressinga change in paper feed speed.

In this embodiment, the roller is a platen roller.

Accordingly, the sheet transport mechanism can reduce errors inengagement of gears when the printing apparatus prints on a sheet whilethe sheet transport mechanism transports the sheet, thereby suppressinga change in paper feed speed.

As described above, according to the density unevenness reduction methodand the sheet transport mechanism in the aspects, errors in engagementof the gears over a long period can be reduced without significantlyimproving the precision of the gears, thereby suppressing a change inpaper feed speed. Accordingly, the printing apparatus including thesheet transport mechanism can reduce the generation of densityunevenness such as jitter without an increase in production costs,thereby obtaining an image with high quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating the main part of a sheettransport mechanism according to an embodiment of the disclosure.

FIG. 2 is a flowchart of a process of setting the module and the numberof teeth of each gear on the basis of a density unevenness reductionmethod according to the embodiment of the disclosure.

FIGS. 3A to 3 c are graphs showing oscillation components in the casewhere one tooth and one turn of each gear in the sheet transportmechanism illustrated in FIG. 1 are represented as a single sine wave.

FIG. 4 is a graph showing a synthesized wave of the sine waves of thegears illustrated in FIGS. 3A to 3C.

FIG. 5 is a graph showing a synthesized wave of the sine waves of gearsin an example of the sheet transport mechanism.

FIG. 6 is a graph showing a synthesized wave of the sine waves of gearsof a sheet transport mechanism.

FIG. 7 is a graph showing a synthesized wave of the sine waves of gearsof a sheet transport mechanism.

FIG. 8 is a graph showing a synthesized wave of the sine waves of gearsof a sheet transport mechanism.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description is intended to convey a thorough understandingof the embodiments described by providing a number of specificembodiments and details involving density unevenness reduction methodand sheet transport. It should be appreciated, however, that the presentinvention is not limited to these specific embodiments and details,which are exemplary only. It is further understood that one possessingordinary skill in the art, in light of known systems and methods, wouldappreciate the use of the invention for its intended purposes andbenefits in any number of alternative embodiments, depending on specificdesign and other needs.

Hereinafter, a density unevenness reduction method according to anembodiment of the invention will be described with reference to FIGS. 1to 8.

FIG. 1 is a perspective view illustrating a sheet transport mechanism 1of a printing apparatus 1 using a density unevenness reduction methodaccording to an embodiment. As illustrated in FIG. 1, the sheettransport mechanism 1 may include, as a roller for transporting a sheetin a predetermined transport direction with rotation, a paper feedroller 2 having a cylindrical shape disposed on the upstream side in thetransport direction from a platen roller (not shown). The paper feedroller 2 may be rotated by the driving of a drive motor as a drivingdevice via a plurality of gears having different gear ratios.

A paper feed gear 3 a of gears 3 may be fixed to an end portion of thepaper feed roller 2, and the paper feed gear 3 a may be engaged with asmall gear (pinion) of a first gear 3 b which may be a double gear. Inaddition, a large gear of the first gear 3 b may be engaged with a smallgear of a second gear 3 c which may be a double gear such that a largegear of the second gear 3 c may be connected to the drive motor as thedriving device (not shown) with a small gear 3 d.

FIG. 2 is a flowchart of a process of setting the module and the numberof teeth of each of the gears 3 on the basis of the density unevennessreduction method. In order to set the module and the number of teeth ofeach of the gears 3, first, a drive motor may be selected, and a torqueneeded for transporting a sheet and the gear ratio of the gears 3 may beset (ST1). Thereafter, the number of stages, the module, and theintermediate gear ratio of each of the gears 3 may be set (ST2), andassuming one tooth and one turn of each gear 3 each to be the simpleharmonic oscillation of a single sine wave, a synthesized wave of thesine waves of the gear 3 may be generated (ST3).

For example, according to this embodiment, in the case where a gearhaving an oscillation period of 0.6 mm pitch is used as the paper feedgear 3 a, a gear having an oscillation period of 0.15 mm pitch is usedas the first gear 3 b, and a gear having an oscillation period of 0.07mm pitch is used as the second gear 3 c, when one tooth and one turn ofeach of the gears 3 are each assumed to be a simple harmonic oscillationof a single sine wave, sine waves as illustrated in FIG. 3A to 3C may beobtained in a graph in which a vertical axis represents an amplitude anda horizontal axis represents a pitch (mm). In addition, when asynthesized wave of the sine waves of the gears 3 is generated, parts inwhich the oscillations of the gears 3 overlap and are amplified occur,and at the same time, parts in which they are attenuated occur, therebyobtaining a synthesized wave having oscillation components asillustrated in FIG. 4.

In addition, it may be determined whether or not the amplitude of thefrequency of the synthesized wave is significant over a long period, andon the basis of the synthesized wave, a density unevenness duringprinting when a sheet may be transported via the gears is predicted(ST4). Whether or not the amplitude of the frequency of the synthesizedwave is significant over a long period may be determined by, forexample, the existence of sharp peaks or regular peaks.

FIGS. 5 to 8 are graphs showing the synthesized waves of the sine wavesof the selected gear 3. As a first example, in the case where a gearhaving an oscillation period of 0.61 mm pitch and a gear having anoscillation period of 0.64 mm pitch are used for the sheet transportmechanism 1, as shown in FIG. 5, the amplitude of the synthesized waveis about ±2, however, the regular oscillation frequency is about 12 mm,so that whizzing for a long period may be predicted. As a secondexample, in the case where the gears 3 having oscillation periods of0.26 mm, 0.46 mm, 0.52 mm, and 0.61 mm pitches are used for the sheettransport mechanism 1, as shown in FIG. 6, the oscillation period of thesynthesized wave is about 1.5 mm, however, the amplitude thereof isabout ±2, and particularly, the amplitude is high in a part indicated byan arrow A, so that frequency dispersion may not be suitable. As a thirdexample, in the case where the gears 3 having oscillation periods of0.23 mm, 0.25 mm, 0.48 mm, and 1.28 mm pitches are used for the sheettransport mechanism 1, as shown in FIG. 7, the amplitude of thesynthesized wave is about ±2, however, the oscillation frequency isabout 3.5 mm, so that frequency dispersion may not be suitable. As afourth example, in the case where the gears 3 having oscillation periodsof 0.058 mm, 0.103 mm, 0.184 mm, and 0.61 mm pitches are used for thesheet transport mechanism 1, as shown in FIG. 8, the amplitude of thesynthesized wave is about ±2, and the oscillation frequency is about 0.5mm, so that sharp peaks or regular peaks do not exist and frequencydispersion may be suitable.

When it is determined that the amplitude of the frequency of thesynthesized wave is significant over a long period (in the case of No inST4), the number of stages, the module, and the intermediate gear ratiomay be re-set (ST2), assuming one tooth and one turn of each gear 3 eachto be the simple harmonic oscillation of a single sine wave, asynthesized wave of the sine waves of the gear 3 is generated (ST3), andit is determined whether the amplitude of the frequency of thesynthesized wave is significant over a long period (ST4). When it isdetermined that the amplitude of the frequency of the synthesized waveis not significant over a long period (in the case of Yes in ST4), withregard to the gears 3, whether or not the sheet transport mechanism 1including the gears 3 can be accommodated in a space set in the printingapparatus (ST5), and when it is determined that the accommodation is notpossible (No in ST5), ST2 to ST4 are repeated. In addition, when it isdetermined that the accommodation is possible in ST5, the module and thenumber of teeth of each gear 3 are set (ST6). As described above, withregard to the sheet transport mechanism 1, on the basis of thesynthesized wave, the module and the number of teeth of each gear 3 areset so that a frequency at which the oscillations of the gears 3 overlapand are amplified is dispersed in the synthesized wave so as not toallow the amplitude of the frequencies of the synthesized wave to besignificant over a long period.

In addition, when the module and the number of teeth of each gear 3 areset, the gear disposed on the upstream side in the transport directionof a sheet among the gears 3 in the sheet transport mechanism 1 may be agear having a period smaller than the period of the sine wave of thegear disposed on the downstream side in the transport direction from thegear. Accordingly, the rotations of the paper feed roller 2 which enablea suitable paper feed speed using the small drive motor having a smalldriving force and fast driving speed via the gears 3 can be obtained.

The sheet transport mechanism 1 may transmit the driving force of thedrive motor to the paper feed roller 2 via the gear 3 to rotate thepaper feed roller 2 for transporting a sheet in a predeterminedtransport direction. The printing apparatus may print on the sheet whiletransporting the sheet using the sheet transport mechanism 1.

According to this embodiment, when the module and the number of teeth ofeach gear 3 of the sheet transport mechanism 1 are set, one tooth andone turn of each gear 3 are each assumed to be a simple harmonicoscillation of a single sine wave, and the synthesized wave of the sinewaves of the gears 3 may be generated. Then, the module and the numberof teeth of each gear 3 may be adjusted so that the frequency at whichthe oscillations of the gears 3 overlap and are amplified may bedispersed in the synthesized wave so as not to allow the amplitude ofthe frequencies of the synthesized wave to be significant over a longperiod. Accordingly, when the printing apparatus prints on the sheetwhile the sheet transport mechanism 1 transports the sheet, errors inengagement of the gears 3 are reduced over a long period, so that achange in paper feed speed can be suppressed.

Therefore, the sheet transport mechanism 1 in which the module and thenumber of teeth of each gear are set by using the density unevennessreduction method according to this embodiment, can reduce errors inengagement of the gears 3 over a long period without significantlyimproving the precision of the gears 3, thereby suppressing a change inpaper feed speed. Accordingly, the printing apparatus including thesheet transport mechanism 1 can reduce the generation of densityunevenness such as jitter without an increase in production costs,thereby obtaining an image with high quality.

In addition, the invention is not limited to the embodiment describedabove, and various modifications can be made as needed.

For example, the embodiment is described by using as the roller used fortransporting a sheet, the paper feed roller 2 which is disposed on theupstream side in the transport direction of the sheet from the platenroller. However, the invention is not limited thereto, and for example,a paper feed roller 2 disposed on the downstream side in the transportdirection from the platen roller, or the platen roller for transportinga sheet may also be applied.

In addition, according to various embodiments, the paper feed gear 3 amay be fixed to the end portion of the paper feed roller 2, however, theinvention is not limited thereto. For example, the paper feed roller 2may be a projection roller on which a plurality of projection teethengaged with the teeth of one of the gears 3 are arranged in parallelwith the circumferential direction of the paper feed roller 2. In thiscase, one tooth and one turn of the paper feed roller 2 are each assumedto be a simple harmonic oscillation of a single sine wave, and thesynthesized wave of the sine waves of the gears 3 and the paper feedroller 2 is generated. Then, the size of the paper feed roller 2 and thenumber of projection teeth may be set so that the frequency at which theoscillation of the gears 3 and the paper feed roller 2 overlap and areamplified is dispersed in the synthesized wave so as to shorten theamplitude of the frequency of the synthesized wave over a long period.Accordingly, errors in engagement of the paper feed roller 2 and thegears 3 are reduced to suppress a change in paper feed speed, so that itis possible to reduce the generation of density unevenness such asjitter in the printing apparatus having the sheet transport mechanism 1.

Accordingly, the embodiments of the present inventions are not to belimited in scope by the specific embodiments described herein. Further,although some of the embodiments of the present invention have beendescribed herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art should recognize that its usefulness is not limited theretoand that the embodiments of the present inventions can be beneficiallyimplemented in any number of environments for any number of purposes.Accordingly, the claims set forth below should be construed in view ofthe full breadth and spirit of the embodiments of the present inventionsas disclosed herein. While the foregoing description includes manydetails and specificities, it is to be understood that these have beenincluded for purposes of explanation only, and are not to be interpretedas limitations of the invention. Many modifications to the embodimentsdescribed above can be made without departing from the spirit and scopeof the invention.

1. A density unevenness reduction method of a printing apparatus havinga sheet transport mechanism which transmits a driving force of a drivingdevice to a roller via a plurality of gears to drive the roller fortransporting a sheet, the method comprising: assuming one tooth and oneturn of each of the gears each to be a simple harmonic oscillation of asingle sine wave, and generating a synthesized wave of the sine waves ofthe gears; and adjusting the module and the number of teeth of each ofthe gears, thereby dispersing a frequency at which the oscillations ofthe gears overlap and are amplified in the synthesized wave.
 2. A sheettransport mechanism comprising: a roller used for transporting a sheet;a driving device for driving the roller; and a plurality of gears fortransmitting a driving force of the driving device to the roller,wherein, assuming one tooth and one turn of each of the gears each to bea simple harmonic oscillation of a single sine wave, a synthesized waveof the sine waves of the gears is generated; and the module and thenumber of teeth of each of the gears are adjusted so as to disperse afrequency at which the oscillations of the gears overlap and areamplified in the synthesized wave and shorten the amplitude of thefrequency of the synthesized wave over a long period.
 3. The sheettransport mechanism according to claim 2, wherein the roller is a paperfeed roller disposed on at least one of the upstream side and thedownstream side of a platen roller in a transport direction of thesheet.
 4. The sheet transport mechanism according to claim 3, whereinthe paper feed roller is configured as a projection roller of which aplurality of projection teeth engaged with the teeth of one of the gearsare arranged in parallel with the circumferential direction of the paperfeed roller, assuming one projection tooth and one turn of the paperfeed roller each to be a simple harmonic oscillation of a single sinewave, a synthesized wave of the sine waves of the gears and the paperfeed roller is generated, and the size of the paper feed roller and thenumber of projection teeth are set so as to disperse a frequency atwhich the oscillations of the gears and the paper feed roller overlapand are amplified in the synthesized wave so as to shorten the amplitudeof the frequency of the synthesized wave over a long period.
 5. Thesheet transport mechanism according to claim 2, wherein the roller is aplaten roller.